Compare the Breathing Rates of a Goldfish and a Human

Fish gills remove oxygen from water as human lungs extract oxygen from air. The oxygen content of air is about 20 times as great as richly aerated water. Therefore, aquatic organisms such as fish spend about 20 times more of their energy breathing than do air breathers.

In this project, you will determine the breathing rates of a goldfish and an air breather (human). Factors affecting the breathing rates, such as temperature changes and physical activity, will be studied. Note: Treat the goldfish with care at all times. Only take on this project if you or someone you know is willing to keep and maintain the fish after the experiments.

Getting Started

Purpose: To observe the opening of a fish's mouth and its operculum (flap of skin covering the gills) to determine the breathing rate of the fish.

Materials

• l-quart (l-liter) jar with wide mouth
• aquarium water
• fishnet
• 5 or more goldfish of different sizes and body markings
• helper
• timer

Procedure

Note: The goldfish should be in an aquarium that has been properly prepared according to instructions from a professional at a pet store or from a fish manual. Feeding of the fish should be considered as part of the normal maintenance of the fish and not as an experiment in this project

1. Prepare a test tank by filling a l-quart (l-liter) jar half full with water from the aquarium.
2. Use the fishnet to carefully transfer the smallest fish from the aquarium to the test jar. Observe the external anatomy of the fish. Record the description and number this fish as 1 in your records so that it can be identified by sight.
3. Wait five minutes to allow the fish to calm after being transferred. Be very quiet and still as you proceed with the experiment.
4. Find the fish's mouth and its operculum (see Figure 21.1).
5. Count the number of times that fish 1 opens and closes its mouth and its operculum over a period of two minutes. Set a timer or ask a helper to assist in timing the experiment.
6. Repeat the counting process (step 5) twice.
7. Average the three trials and divide by 2 to determine the average breathing rate (number of mouth/operculum openings) for one minute. A two-minute observation time is used because small fluctuations are averaged out with longer observation periods.
8. Use the fishnet to carefully return the fish to the aquarium.

Results

The mouth and the operculum open and close an equal number of times. The breathing rate per minute may vary but should be between 100 and 115.

Why?

A fish inhales water; it does not drink water. ''Yawning'' movements draw water into the mouth, and then the mouth closes. The mouth cavity contracts, forcing the water through the gills and out the operculum, the protective covering over the gills. This rhythmic movement of the mouth and operculum brings in oxygen-rich water to the gills, where the oxygen is extracted. The oxygen-depleted water is then expelled through the operculum.

Try New Approaches

Does the size of the fish affect its breathing rate? Observe the external anatomy of the other goldfish as they swim in the aquarium. Record descriptions of each fish and number them in order of size (smallest as number 1) in your records so that each can be identified by sight. Repeat the experiment for each of the fish. Science Fair Hint: Take photographs of each fish to use as part of your display. Provide information about the breathing rate of each.

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